Throughout the Anthropocene, urbanization has changed the environment for birds, modifying the types and abundance of available materials to build their nests. Discarded plastics and other anthropogenic materials are very abundant in urbanized and agricultural areas and are being used by birds to build nests, constituting a potential threat to them. Objective: To evaluate the materials used for several species of birds living in an urbanized environment. Methods: We evaluated the composition of 20 nests of several species of birds found in the campus of Universidad Nacional. Results: 52.6% of nests contained some sort of waste classified in 13 types of anthropogenic materials, where the most common were wool, strings and thread. The species with the highest percentage of nest weight comprised by anthropogenic material was Campylorhynchus rufinucha Conclusions: Our results demonstrates the widespread use of anthropogenic waste as nesting material.

Spiders show a repertoire of strategies to increase their foraging success. In particular, some orb-weaver spiders use attractive body colorations to lure prey. Interestingly, coloration varies with age in many species, which may result in ontogenetic variation of foraging success. By using field observations, laboratory experiments and spectrophotometric analysis, we investigated whether pale juveniles and bright adults of the orb-weaver Alpaida tuonabo use different foraging strategies due to ontogenetic variation in coloration. Field observations revealed that foraging success of juveniles and adults was influenced by web properties. However, foraging success increased with body size only in adults, supporting the idea that larger individuals produce a stronger visual signal for prey. The attractiveness of the adult coloration for prey was confirmed in the laboratory with frame-web-choice experiments, in which webs bearing a spider intercepted more bees than empty webs. Our spectrophotometric analysis suggests that the yellow coloration may produce the deceiving signal for prey. Moreover, we identified potential alternative foraging strategies: cryptic juveniles at higher heights and ‘attractive’ adults at lower heights. This study reveals how ontogenetic colour variation may favour the use of alternative foraging strategies in orb-weaver spiders and reduces intraspecific competition.